Near the southern tip of Greenland, lies the old mining town of Ivittuut, now a collection of ramshackle houses and sheds and scattered pieces of old machinery. Ivittuut was once the world’s largest source of cryolite, an extremely rare mineral that was historically used in the extraction of aluminium from bauxite ore. Although cryolite has been found at other places on earth, Ivittuut was the only place where this mineral was extracted commercially.
Cryolite was first discovered in Ivittuut in 1799 by British miners who were engaged in silver mining around the town. But the silver content in the veins were too low to make the operation profitable, and mining was abandoned. Sixty years later, Danish engineers began mining cryolite for its aluminum content.
An abandoned house in Ivittuut, in Greenland. Image credit: S. Bonaime/Shutterstock.com
Cryolite, or sodium hexafluoroaluminate, is a colorless compound containing sodium, fluorine and aluminium. The name is derived from the Greek words κρυος (cryos) meaning “ice”, and λιθος (lithos) meaning “stone”.
The aluminium content of cryolite is only 13 per cent, compared to 50 percent in bauxite, the major source of aluminium in the world today. Bauxite is also relatively common, but extracting the metal out of the mineral on an industrial scale turned out to be tricky. It was recognized early on that the way to do this was to pass an electric current through the molten ore, a technique known as electrolysis. But bauxite melts at a very temperature, in excess of 2000°C, which made electrolysis impractical and cost prohibitive.
In 1886, an American chemist named Charles Martin Hall and a Frenchman, Paul Héroult, independently discovered at almost the same time that if a tiny bit of cryolite is added to the bauxite solution, it lowers the melting point of the aluminium ore to less than 1000 °C. Besides lowering the melting point, cryolite also helps dissolves alumina well, improves the conductivity of the solution and allows electrolysis to be carried at a much higher voltage. This is the Hall–Héroult process.
Cryolite: Image credit: James St. John/Flickr
The Hall–Héroult process turned aluminium from a precious metal into an inexpensive commodity. Prices of aluminium dropped and aluminium became a part of everyday life in the form of jewelry, utensils, eyeglass frames, optical instruments, tableware, and so on. Aluminium's ability to form hard yet light alloys with other metals made aluminium a major material for airplane construction.
During World War 2, when Germany occupied Denmark, the Allies sent a platoon to Ivittuut to protect the mine from the Nazis because of its importance in airplane production. To strengthen its hold, the US Navy built a naval base three miles away in Kangilinnguit, and the US Coast Guard built a base across the fjord from Ivittuut, holding hundreds more soldiers. To protect its location, no photographs of Ivittuut were allowed to be taken during the war, and no one was allowed to write letters to family or friends for fear that the Germans would intercept them.
After the war, Denmark continued to mine cryolite until the mines were exhausted in the late 1980s. The mine closed in 1987.
Today, cryolite is substituted with synthetically produced sodium aluminium fluoride in the Hall–Héroult process, which is still used to this day to produce aluminium.
The cryolite quarry at Ivittuut.
The cryolite quarry at Ivittuut.
Image credit: Mindat.org
